Well ok, so now we can detect some nice geometrical shapes, but we haven't really related it to the game of Go as such. To do that we need to teach the computer a bit about the rules, so that it can at least process the effects of a move, and determine whether a proposed move is legal or not.
Fortunately Go has very few rules - all the complexity flows from their application.
So, here are the basics:
1) The game has two players, one taking the black stones, the other the white.
2) Players take alternating turns, beginning with black. On each turn a player places one stone of his or her own colour on a vacant intersection of the board. A player may choose to pass rather than play if they wish to.
3) Stones are captured if they have no liberties. To define what this means we need to talk a bit about some basic concepts. I'll do that in a moment. First lets quickly finish up on the remaining rules
4) It is illegal to play a stone in such a way that it would immediately have no liberties unless by doing so it captures one or more opposing stones and thus gains one or more liberties in the resulting position (no suicide)
5) It is illegal to play in such a way as to repeat a previous position (strictly this is a generalised variant of a slightly harder-to-state rule called the 'ko' rule, but we'll just go with the easier-to-understand generalisation (which means we'll be playing what are called 'Chineese rules'))
6) The game terminates after 3 consecutive passes, after which the winner is determined by adding up the territory owned by each player + any captured stones they have gained during play (more on territory below)
So this all boils down to two concepts, which need better definition:
Captured stones are removed from the board, and each counts as one point when the scores are determined at the end of the game.
The final concept we need then is territory. At the end of the game players agree which stones that have not actually been captured are anyway 'dead' (what this boils down to is stones which both players agree would be captured regardless of anything the owning player could do if they chose to play things out locally). A simple example of a dead stone is shown below - because it is obviously futile for white to play further stones (each of which will ultimately be one more point for his opponent when eventually captured) he will not do so. In the event of a disagreement between the players over what is dead, the onus is on the player claiming they are not to demonstrate he can forms two eyes (see below) and thus avoid capture).
Once all dead stones are removed each vacant point entirely surrounded by one colour is a point of territory for the player enclosing it. A player's territory + captures is their final score. The white player often (though this is more an adjunct than a rule really) is also awarded what is known as a komi, or extra points to compensate for black's advantage in having the first move. A typical komi (which may vary from tournament to tournament) is 5.5 points (thus avoiding draws).
Finally to illustrate rule (5) (no repeated positions) take a look at this position: